Tetsuya Kimura - Academia.edu (original) (raw)

Papers by Tetsuya Kimura

Neuroscience Letters, 2017

Microtubule-associated protein tau has crucial roles not only in the formation of some neurodegen... more Microtubule-associated protein tau has crucial roles not only in the formation of some neurodegenerative disorders but also in normal synaptic functions, although its contributions to these are still unclear. Here, to reveal the influence of tau deletion on trafficking of synaptic receptors, we investigated the distribution of GluA2-containing AMPA-type glutamate receptors (AMPARs) within neuronal dendrites in wild-type and tau-deficient neurons using biochemical and laser-confocal imaging techniques. Under basal conditions, expression of GluA2 at tau-deficient synapses was almost normal; however, its level within dendrites in tau-deficient neurons was greater than that in wild-type neurons. After NMDA treatment, a decrease in GluA2-containing AMPARs at synapses was observed in wild-type neurons, but not in tau-deficient neurons. Single-cell imaging of GluA2 within dendrites demonstrated that wild-type neurons, but not tau-deficient neurons, showed enlargement of GluA2 puncta. Interestingly, we also found that NMDA rapidly reduced the number of GluA2 puncta without changing their size in tau-deficient neurons but not wild-type neurons. These results demonstrate the multiple contributions of tau to the maintenance of dynamic AMPAR trafficking within dendrites during both stimulated and unstimulated conditions.

Neuroscience Research, 1998

Neuroscience Letters, 2001

We studied the neural oscillatory activity in the peripheral olfactory system of the tentacles in... more We studied the neural oscillatory activity in the peripheral olfactory system of the tentacles in the terrestrial slug, Limax marginatus, by extracellular recording. Recordings from the cut-ends of the inferior tentacular nerves connected to the inferior tentacular ganglia and sensory epithelia showed spontaneous oscillatory activity at frequencies of 0.1±30 Hz. This spontaneous activity was dominated by the 0.6±6 Hz band. Ethanol odor stimulation decreased the amplitude in the 0.6±6 Hz band and increased those in the 6±15 and 15±30 Hz bands. Antagonists of the g-aminobutyric acid (GABA) receptor, bicuculline and picrotoxin, resulted in suppression of spontaneous activity and modulated the odor response in the 0.6±6 Hz band. Our results indicate the involvement of GABA-mediated oscillatory activity in the tentacular nerves in the olfactory processing in molluscs.

The American Journal of Pathology, 2013

Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) is a neurodegenerative... more Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) is a neurodegenerative disorder caused by mutations in the tau gene. Many mutations identified in FTDP-17 have been shown to affect tau exon 10 splicing in vitro, which presumably causes pathologic imbalances in exon 10(-) [3-repeat (3R)] and exon 10(+) [4-repeat (4R)] tau expression and leads to intracellular inclusions of hyperphosphorylated tau in patient brains. However, no reports have investigated this theory using model mice with a tau intronic mutation. Herein, we generated new transgenic mice harboring the tau intron 10 +16C → T mutation. We prepared a transgene construct containing intronic sequences required for exon 10 splicing in the longest tau isoform cDNA. Although mice bearing the construct without the intronic mutation showed normal developmental changes of the tau isoform from 3R tau to equal amounts of 3R and 4R tau, mice with the mutation showed much higher levels of 4R tau at the adult stage. 4R tau was selectively recovered in insoluble brain fractions in their old age. Furthermore, these mice displayed abnormal tau phosphorylation, synapse loss and dysfunction, memory impairment, glial activation, tangle formation, and neuronal loss in an age-dependent manner. These findings provide the first evidence in a mouse model that a tau intronic mutation-induced imbalance of 3R and 4R tau could be a cause of tauopathy.

Journal of Biological Chemistry, 2005

Mutations in the presenilin 1 (PS1) gene are responsible for the early onset of familial Alzheime... more Mutations in the presenilin 1 (PS1) gene are responsible for the early onset of familial Alzheimer disease (FAD). Accumulating evidence shows that PS1 is involved in ␥-secretase activity and that FAD-associated mutations of PS1 commonly accelerate A␤ 1-42 production, which causes Alzheimer disease (AD). Recent studies suggest, however, that PS1 is involved not only in A␤ production but also in other processes that lead to neurodegeneration. To better understand the causes of neurodegeneration linked to the PS1 mutation, we analyzed the development of tau pathology, another key feature of AD, in PS1 knock-in mice. Hippocampal samples taken from FAD mutant (I213T) PS1 knock-in mice contained hyperphosphorylated tau that reacted with various phosphodependent tau antibodies and with Alz50, which recognizes the conformational change of PHF tau. Some neurons exhibited Congo red birefringence and Thioflavin T reactivity, both of which are histological criteria for neurofibrillary tangles (NFTs). Biochemical analysis of the samples revealed SDS-insoluble tau, which under electron microscopy examination, resembled tau fibrils. These results indicate that our mutant PS1 knock-in mice exhibited NFT-like tau pathology in the absence of A␤ deposition, suggesting that PS1 mutations contribute to the onset of AD not only by enhancing A␤ 1-42 production but by also accelerating the formation and accumulation of filamentous tau.

Neurofibrillary tangles (NFTs), which consist of highly phosphorylated tau, are hallmarks of neur... more Neurofibrillary tangles (NFTs), which consist of highly phosphorylated tau, are hallmarks of neurodegenerative diseases including Alzheimer disease (AD). In neurodegenerative diseases, neuronal dysfunction due to neuronal loss and synaptic loss accompanies NFT formation, suggesting that a process associated with NFT formation may be involved in neuronal dysfunction. To clarify the relationship between the tau aggregation process and synapse and neuronal loss, we compared two lines of mice expressing human tau with or without an aggregation-prone P301L mutation. P301L tau transgenic (Tg) mice exhibited neuronal loss and produced sarcosyl-insoluble tau in old age but did not exhibit synaptic loss and memory impairment. By contrast, wild-type tau Tg mice neither exhibited neuronal loss nor produced sarcosyl-insoluble tau but did exhibit synaptic loss and memory impairment. Moreover, P301L tau was less phosphorylated than wild-type tau, suggesting that the tau phosphorylation state is involved in synaptic loss, whereas the tau aggregation state is involved in neuronal loss. Finally, increasing concentrations of insoluble tau aggregates leads to the formation of fibrillar tau, which causes NFTs to form.

Acta Neuropathologica Communications

The aggregation mechanism of phosphorylated tau is an important therapeutic target for tauopathie... more The aggregation mechanism of phosphorylated tau is an important therapeutic target for tauopathies, including Alzheimer's disease, although the mechanism by which aggregation occurs is still unknown. Because the phosphorylation process of tau is involved in the trafficking of AMPA receptors, which accompanies the long-term depression (LTD) of synapses, we examined the effect of LTD-inducing low-frequency stimulation (LFS) on the formation of pathological tau aggregates in adult and aged wild-type mice. Our biochemical analysis demonstrated that LFS led to the formation of sarkosyl-insoluble (SI) tau oligomers in aged hippocampi but not in adult hippocampi in wild-type mice. In parallel, electrophysiological experiments showed an increased contribution of the autophagy-lysosomal pathway (ALP) to LTD during aging, although the other properties of LFS-induced LTD that we investigated were not altered. Thus, we anticipate that the increased contribution of the ALP to the LTD cascade is involved in the age-dependent formation of tau oligomers that results from LFS. Analysis of the LC3 ratio, an indicator of autophagosome formation, showed that LFS increased cleaved LC3 (type II) in the aged hippocampus relative to type I LC3, suggesting potentiation of the ALP accompanied by LTD. Pharmacological inhibition of autophagosome formation depressed LFSinduced oligomerization of tau. Prevention of lysosomal function in the ALP enhanced the formation of tau oligomers by LFS. These results suggest the importance of the autophagosome for the LFS-induced oligomerization of tau and suggest a reason for its age dependency. Interestingly, the lysosomal disturbance promoted the formation of the fibrillar form of aggregates consisting of hyper-phosphorylated tau. The LTD-ALP cascade potentially acts as one of the suppliers of pathological aggregates of tau in aged neurons.

Acta neuropathologica communications, Jan 31, 2017

The E693Δ (Osaka) mutation in APP is linked to familial Alzheimer's disease. While this mutat... more The E693Δ (Osaka) mutation in APP is linked to familial Alzheimer's disease. While this mutation accelerates amyloid β (Aβ) oligomerization, only patient homozygotes suffer from dementia, implying that this mutation is recessive and causes loss-of-function of amyloid precursor protein (APP). To investigate the recessive trait, we generated a new mouse model by knocking-in the Osaka mutation into endogenous mouse APP. The produced homozygous, heterozygous, and non-knockin littermates were compared for memory, neuropathology, and synaptic plasticity. Homozygotes showed memory impairment at 4 months, whereas heterozygotes did not, even at 8 months. Immunohistochemical and biochemical analyses revealed that only homozygotes displayed intraneuronal accumulation of Aβ oligomers at 8 months, followed by abnormal tau phosphorylation, synapse loss, glial activation, and neuron loss. These pathologies were not observed at younger ages, suggesting that a certain mechanism other than Aβ acc...

Tau-mediated neurodegeneration is a central event in Alzheimer's disease (AD) and other tauopathi... more Tau-mediated neurodegeneration is a central event in Alzheimer's disease (AD) and other tauopathies. Consistent with suggestions that lifetime stress may be a clinically-relevant precipitant of AD pathology, we previously showed that stress triggers Tau hyperphosphorylation and accumulation; however, little is known about the etiopathogenic interaction of chronic stress with other AD risk factors, such as sex and aging. This study focused on how these various factors converge on the cellular mechanisms underlying Tau aggregation in the hippocampus of chronically stressed male and female (middle-aged and old) mice expressing the most commonly found disease-associated Tau mutation in humans, P301L-Tau. We report that environmental stress triggers memory impairments in female, but not male, P301L-Tau transgenic mice. Furthermore, stress elevates levels of caspase-3-truncated Tau and insoluble Tau aggregates exclusively in the female hippocampus while it also alters the expression of the molecular chaperones Hsp90, Hsp70, and Hsp105, thus favoring accumulation of Tau aggregates. Our findings provide new insights into the molecular mechanisms through which clinically-relevant precipitating factors contribute to the pathophysiology of AD. Our data point to the exquisite sensitivity of the female hippocampus to stress-triggered Tau pathology.

Zoological Science, 2003

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Zoological Science, 1999

As the first step to study relationships between development and learning in the molluscan centra... more As the first step to study relationships between development and learning in the molluscan central nervous system, we examined developmental changes in acquisition and retention of a conditioned taste aversion (CTA) in the pond snail, Lymnaea stagnalis. We found that snails developed ability of a CTA as a long-term memory through three critical stages. Embryos in veliconcha started to respond to appetitive sucrose at the first critical stage. This response was in good agreement with morphological observations that embryos at this developmental stage seemed to be physically ready to eat. However, they could not associate this appetitive stimulus (conditioned stimulus: CS) with an aversive stimulus of KCl (unconditioned stimulus: UCS). At the second critical stage, embryos just before hatching acquired the CTA, but the conditioned response did not persist. Through this stage, they may acquire learning ability to safely seek out food in an external environment. At the third critical stage, immature snails with a 10 mm shell could use a long-term memory to maintain the conditioned response. This memory persisted for at least a month, showing that now they are able to maintain a long-term memory so that they can safely eat a variety of food when they cover wide territory to search for a mate. The present findings indicate that the development of learning ability in snails, which secures acquisition of better survival ability, is coincident with the major changes in their life cycle.

PLoS ONE, 2011

Squid can rapidly change the chromatic patterns on their body. The patterns are created by the ex... more Squid can rapidly change the chromatic patterns on their body. The patterns are created by the expansion and retraction of chromatophores. The chromatophore consists of a central pigment-containing cell surrounded by radial muscles that are controlled by motor neurons located in the central nervous system (CNS). In this study we used semi-intact squid (Sepioteuthis lessoniana) displaying centrally controlled natural patterns to analyze spatial and temporal activities of chromatophores located on the dorsal mantle skin. We found that chromatophores oscillated with miniature expansions/ retractions at various frequencies, even when the chromatic patterns appear macroscopically stable. The frequencies of this miniature oscillation differed between ''feature'' and ''background'' areas of chromatic patterns. Higher frequencies occurred in feature areas, whereas lower frequencies were detected in background areas. We also observed synchronization of the oscillation during chromatic pattern expression. The expansion size of chromatophores oscillating at high frequency correlated with the number of synchronized chromatophores but not the oscillation frequency. Miniature oscillations were not observed in denervated chromatophores. These results suggest that miniature oscillations of chromatophores are driven by motor neuronal activities in the CNS and that frequency and synchrony of this oscillation determine the chromatic pattern and the expansion size, respectively.

PLoS ONE, 2009

Background: The M 5 muscarinic acetylcholine receptor is known to play a crucial role in mediatin... more Background: The M 5 muscarinic acetylcholine receptor is known to play a crucial role in mediating acetylcholine dependent dilation of cerebral blood vessels. Previously, we reported that male M 5 muscarinic acetylcholine knockout mice (M5R 2/2 mice) suffer from a constitutive constriction of cerebral arteries, reduced cerebral blood flow, dendritic atrophy, and shortterm memory loss, without necrosis and/or inflammation in the brain. Methodology/Principal Findings: We employed the Magnetic Resonance Angiography to study the area of the basilar artery in male and female M5R 2/2 mice. Here we show that female M5R 2/2 mice did not show the reduction in vascular area observed in male M5R 2/2 mice. However, ovariectomized female M5R 2/2 mice displayed phenotypic changes similar to male M5R 2/2 mice, strongly suggesting that estrogen plays a key role in the observed gender differences. We found that 17b-estradiol (E2) induced nitric oxide release and ERK activation in a conditional immortalized mouse brain cerebrovascular endothelial cell line. Agonists of ERa, ERb, and GPR30 promoted ERK activation in this cell line. Moreover, in vivo magnetic resonance imaging studies showed that the cross section of the basilar artery was restored to normal in male M5R 2/2 mice treated with E2. Treatment with E2 also improved the performance of male M5R 2/2 mice in a cognitive test and reduced the atrophy of neural dendrites in the cerebral cortex and hippocampus. M5R 2/2 mice also showed astrocyte swelling in cortex and hippocampus using the three-dimensional reconstruction of electron microscope images. This phenotype was reversed by E2 treatment, similar to the observed deficits in dendrite morphology and the number of synapses. Conclusions/Significance: Our findings indicate that M5R 2/2 mice represent an excellent novel model system to study the beneficial effects of estrogen on cerebrovascular function and cognition. E2 may offer new therapeutic perspectives for the treatment of cerebrovascular insufficiency related memory dysfunction.

Learning & Memory, 1998

To determine the distribution of neurons that contribute to memory formation induced by odor-tast... more To determine the distribution of neurons that contribute to memory formation induced by odor-taste associative conditioning in the slug's brain, we examined neuronal activity of the central nervous system of the slug Limax marginatus using a fluorescent activity marker [Lucifer yellow (LY)]. When LY was injected into the body cavity just after the conditioning, many of the procerebral (PC) interneurons were labeled. The PC lobe was considered to play important roles in the olfaction of the slug, because the olfactory afferent fibers from both the inferior and the superior tentacular noses innervate it. Such strong dye-uptake activity of PC interneurons was not observed when LY was injected just after unpaired control treatment. Thus, it was suggested that enhancement of dye-uptake activity upon conditioning was caused by the association of a conditioning stimulus (CS) with an unconditioned stimulus (UCS). The distribution patterns of PC interneurons that were labeled by LY after...

Learning & Memory, 1998

We compared behaviorally and physiologically the olfactory responses of slugs (Limax marginatus) ... more We compared behaviorally and physiologically the olfactory responses of slugs (Limax marginatus) that had been subjected to aversive, appetitive, or unpaired training with food odors (carrot or cucumber). In the aversive training, the slugs were exposed to the food odor as a conditioned stimulus (CS), and then quinidine sulfate solution as an unconditioned stimulus (UCS) was immediately applied to the lip of the slugs. This training caused a decrease in preference level for the CS. The unpaired training, in which the CS and the UCS were presented to the slugs with a 5-min interval, induced no change in the preference level for the CS. In the appetitive training, the slugs were allowed to eat the CS odor source without UCS application. When we used nonstarved slugs, it was found that the preference level for the CS increased upon the appetitive training. These results indicate that each training changed the preference for the odors in a characteristic manner. In the physiological exp...

PloS one, 2008

PLoS ONE: an inclusive, peer-reviewed, open-access resource from the PUBLIC LIBRARY OF SCIENCE. R... more PLoS ONE: an inclusive, peer-reviewed, open-access resource from the PUBLIC LIBRARY OF SCIENCE. Reports of well-performed scientific studies from all disciplines freely available to the whole world.

Activation of GSK-3b is presumed to be involved in various neurodegenerative diseases, including ... more Activation of GSK-3b is presumed to be involved in various neurodegenerative diseases, including Alzheimer's disease (AD), which is characterized by memory disturbances during early stages of the disease. The normal function of GSK-3b in adult brain is not well understood. Here, we analyzed the ability of heterozygote GSK-3b knockout (GSK+/2) mice to form memories. In the Morris water maze (MWM), learning and memory performance of GSK+/2 mice was no different from that of wild-type (WT) mice for the first 3 days of training. With continued learning on subsequent days, however, retrograde amnesia was induced in GSK+/2 mice, suggesting that GSK+/2 mice might be impaired in their ability to form long-term memories. In contextual fear conditioning (CFC), context memory was normally consolidated in GSK+/2 mice, but once the original memory was reactivated, they showed reduced freezing, suggesting that GSK+/2 mice had impaired memory reconsolidation. Biochemical analysis showed that GSK-3b was activated after memory reactivation in WT mice. Intraperitoneal injection of a GSK-3 inhibitor before memory reactivation impaired memory reconsolidation in WT mice. These results suggest that memory reconsolidation requires activation of GSK-3b in the adult brain.

Background: Tauopathies are characterized by intracellular deposition of the microtubule-associat... more Background: Tauopathies are characterized by intracellular deposition of the microtubule-associated protein tau as filamentous aggregates. The rTg4510 mouse conditionally expresses mutant human tau protein in various forebrain areas under the Tet-off expression system. Mice develop neurofibrillary tangles, with significant neuronal loss and cognitive deficits by 6 months of age. Previous behavioral and biochemical work has linked the expression and aggregates of mutant tau to functional impairments. The present work used manganese-enhanced magnetic resonance imaging (MEMRI) to investigate basal levels of brain activity in the rTg4510 and control mice. Results: Our results show an unmistakable curtailment of neural activity in the amygdala and hippocampus, two regions known for their role in memory formation, but not the cortex, cerebellum, striatum and hypothalamus in tau expressing mice. Conclusion: Behavioral impairments associated with changes in activity in these areas may correspond to age progressive mutant tau P301L-induced neurodegeneration.

PloS one, 2014

In recent years, the study of resting state neural activity has received much attention. To bette... more In recent years, the study of resting state neural activity has received much attention. To better understand the roles of different brain regions in the regulation of behavioral activity in an arousing or a resting period, we developed a novel behavioral paradigm (8-arm food-foraging task; 8-arm FFT) using the radial 8-arm maze and examined how AcbC lesions affect behavioral execution and learning. Repetitive training on the 8-arm FFT facilitated motivation of normal rats to run quickly to the arm tips and to the center platform before the last-reward collection. Importantly, just after this point and before confirmation of no reward at the next arm traverse, locomotor activity decreased. This indicates that well-trained rats can predict the absence of the reward at the end of food seeking and then start another behavior, namely planned resting. Lesions of the AcbC after training selectively impaired this reduction of locomotor activity after the last-reward collection without chan...

Neuroscience Letters, 2017

Microtubule-associated protein tau has crucial roles not only in the formation of some neurodegen... more Microtubule-associated protein tau has crucial roles not only in the formation of some neurodegenerative disorders but also in normal synaptic functions, although its contributions to these are still unclear. Here, to reveal the influence of tau deletion on trafficking of synaptic receptors, we investigated the distribution of GluA2-containing AMPA-type glutamate receptors (AMPARs) within neuronal dendrites in wild-type and tau-deficient neurons using biochemical and laser-confocal imaging techniques. Under basal conditions, expression of GluA2 at tau-deficient synapses was almost normal; however, its level within dendrites in tau-deficient neurons was greater than that in wild-type neurons. After NMDA treatment, a decrease in GluA2-containing AMPARs at synapses was observed in wild-type neurons, but not in tau-deficient neurons. Single-cell imaging of GluA2 within dendrites demonstrated that wild-type neurons, but not tau-deficient neurons, showed enlargement of GluA2 puncta. Interestingly, we also found that NMDA rapidly reduced the number of GluA2 puncta without changing their size in tau-deficient neurons but not wild-type neurons. These results demonstrate the multiple contributions of tau to the maintenance of dynamic AMPAR trafficking within dendrites during both stimulated and unstimulated conditions.

Neuroscience Research, 1998

Neuroscience Letters, 2001

We studied the neural oscillatory activity in the peripheral olfactory system of the tentacles in... more We studied the neural oscillatory activity in the peripheral olfactory system of the tentacles in the terrestrial slug, Limax marginatus, by extracellular recording. Recordings from the cut-ends of the inferior tentacular nerves connected to the inferior tentacular ganglia and sensory epithelia showed spontaneous oscillatory activity at frequencies of 0.1±30 Hz. This spontaneous activity was dominated by the 0.6±6 Hz band. Ethanol odor stimulation decreased the amplitude in the 0.6±6 Hz band and increased those in the 6±15 and 15±30 Hz bands. Antagonists of the g-aminobutyric acid (GABA) receptor, bicuculline and picrotoxin, resulted in suppression of spontaneous activity and modulated the odor response in the 0.6±6 Hz band. Our results indicate the involvement of GABA-mediated oscillatory activity in the tentacular nerves in the olfactory processing in molluscs.

The American Journal of Pathology, 2013

Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) is a neurodegenerative... more Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) is a neurodegenerative disorder caused by mutations in the tau gene. Many mutations identified in FTDP-17 have been shown to affect tau exon 10 splicing in vitro, which presumably causes pathologic imbalances in exon 10(-) [3-repeat (3R)] and exon 10(+) [4-repeat (4R)] tau expression and leads to intracellular inclusions of hyperphosphorylated tau in patient brains. However, no reports have investigated this theory using model mice with a tau intronic mutation. Herein, we generated new transgenic mice harboring the tau intron 10 +16C → T mutation. We prepared a transgene construct containing intronic sequences required for exon 10 splicing in the longest tau isoform cDNA. Although mice bearing the construct without the intronic mutation showed normal developmental changes of the tau isoform from 3R tau to equal amounts of 3R and 4R tau, mice with the mutation showed much higher levels of 4R tau at the adult stage. 4R tau was selectively recovered in insoluble brain fractions in their old age. Furthermore, these mice displayed abnormal tau phosphorylation, synapse loss and dysfunction, memory impairment, glial activation, tangle formation, and neuronal loss in an age-dependent manner. These findings provide the first evidence in a mouse model that a tau intronic mutation-induced imbalance of 3R and 4R tau could be a cause of tauopathy.

Journal of Biological Chemistry, 2005

Mutations in the presenilin 1 (PS1) gene are responsible for the early onset of familial Alzheime... more Mutations in the presenilin 1 (PS1) gene are responsible for the early onset of familial Alzheimer disease (FAD). Accumulating evidence shows that PS1 is involved in ␥-secretase activity and that FAD-associated mutations of PS1 commonly accelerate A␤ 1-42 production, which causes Alzheimer disease (AD). Recent studies suggest, however, that PS1 is involved not only in A␤ production but also in other processes that lead to neurodegeneration. To better understand the causes of neurodegeneration linked to the PS1 mutation, we analyzed the development of tau pathology, another key feature of AD, in PS1 knock-in mice. Hippocampal samples taken from FAD mutant (I213T) PS1 knock-in mice contained hyperphosphorylated tau that reacted with various phosphodependent tau antibodies and with Alz50, which recognizes the conformational change of PHF tau. Some neurons exhibited Congo red birefringence and Thioflavin T reactivity, both of which are histological criteria for neurofibrillary tangles (NFTs). Biochemical analysis of the samples revealed SDS-insoluble tau, which under electron microscopy examination, resembled tau fibrils. These results indicate that our mutant PS1 knock-in mice exhibited NFT-like tau pathology in the absence of A␤ deposition, suggesting that PS1 mutations contribute to the onset of AD not only by enhancing A␤ 1-42 production but by also accelerating the formation and accumulation of filamentous tau.

Neurofibrillary tangles (NFTs), which consist of highly phosphorylated tau, are hallmarks of neur... more Neurofibrillary tangles (NFTs), which consist of highly phosphorylated tau, are hallmarks of neurodegenerative diseases including Alzheimer disease (AD). In neurodegenerative diseases, neuronal dysfunction due to neuronal loss and synaptic loss accompanies NFT formation, suggesting that a process associated with NFT formation may be involved in neuronal dysfunction. To clarify the relationship between the tau aggregation process and synapse and neuronal loss, we compared two lines of mice expressing human tau with or without an aggregation-prone P301L mutation. P301L tau transgenic (Tg) mice exhibited neuronal loss and produced sarcosyl-insoluble tau in old age but did not exhibit synaptic loss and memory impairment. By contrast, wild-type tau Tg mice neither exhibited neuronal loss nor produced sarcosyl-insoluble tau but did exhibit synaptic loss and memory impairment. Moreover, P301L tau was less phosphorylated than wild-type tau, suggesting that the tau phosphorylation state is involved in synaptic loss, whereas the tau aggregation state is involved in neuronal loss. Finally, increasing concentrations of insoluble tau aggregates leads to the formation of fibrillar tau, which causes NFTs to form.

Acta Neuropathologica Communications

The aggregation mechanism of phosphorylated tau is an important therapeutic target for tauopathie... more The aggregation mechanism of phosphorylated tau is an important therapeutic target for tauopathies, including Alzheimer's disease, although the mechanism by which aggregation occurs is still unknown. Because the phosphorylation process of tau is involved in the trafficking of AMPA receptors, which accompanies the long-term depression (LTD) of synapses, we examined the effect of LTD-inducing low-frequency stimulation (LFS) on the formation of pathological tau aggregates in adult and aged wild-type mice. Our biochemical analysis demonstrated that LFS led to the formation of sarkosyl-insoluble (SI) tau oligomers in aged hippocampi but not in adult hippocampi in wild-type mice. In parallel, electrophysiological experiments showed an increased contribution of the autophagy-lysosomal pathway (ALP) to LTD during aging, although the other properties of LFS-induced LTD that we investigated were not altered. Thus, we anticipate that the increased contribution of the ALP to the LTD cascade is involved in the age-dependent formation of tau oligomers that results from LFS. Analysis of the LC3 ratio, an indicator of autophagosome formation, showed that LFS increased cleaved LC3 (type II) in the aged hippocampus relative to type I LC3, suggesting potentiation of the ALP accompanied by LTD. Pharmacological inhibition of autophagosome formation depressed LFSinduced oligomerization of tau. Prevention of lysosomal function in the ALP enhanced the formation of tau oligomers by LFS. These results suggest the importance of the autophagosome for the LFS-induced oligomerization of tau and suggest a reason for its age dependency. Interestingly, the lysosomal disturbance promoted the formation of the fibrillar form of aggregates consisting of hyper-phosphorylated tau. The LTD-ALP cascade potentially acts as one of the suppliers of pathological aggregates of tau in aged neurons.

Acta neuropathologica communications, Jan 31, 2017

The E693Δ (Osaka) mutation in APP is linked to familial Alzheimer's disease. While this mutat... more The E693Δ (Osaka) mutation in APP is linked to familial Alzheimer's disease. While this mutation accelerates amyloid β (Aβ) oligomerization, only patient homozygotes suffer from dementia, implying that this mutation is recessive and causes loss-of-function of amyloid precursor protein (APP). To investigate the recessive trait, we generated a new mouse model by knocking-in the Osaka mutation into endogenous mouse APP. The produced homozygous, heterozygous, and non-knockin littermates were compared for memory, neuropathology, and synaptic plasticity. Homozygotes showed memory impairment at 4 months, whereas heterozygotes did not, even at 8 months. Immunohistochemical and biochemical analyses revealed that only homozygotes displayed intraneuronal accumulation of Aβ oligomers at 8 months, followed by abnormal tau phosphorylation, synapse loss, glial activation, and neuron loss. These pathologies were not observed at younger ages, suggesting that a certain mechanism other than Aβ acc...

Tau-mediated neurodegeneration is a central event in Alzheimer's disease (AD) and other tauopathi... more Tau-mediated neurodegeneration is a central event in Alzheimer's disease (AD) and other tauopathies. Consistent with suggestions that lifetime stress may be a clinically-relevant precipitant of AD pathology, we previously showed that stress triggers Tau hyperphosphorylation and accumulation; however, little is known about the etiopathogenic interaction of chronic stress with other AD risk factors, such as sex and aging. This study focused on how these various factors converge on the cellular mechanisms underlying Tau aggregation in the hippocampus of chronically stressed male and female (middle-aged and old) mice expressing the most commonly found disease-associated Tau mutation in humans, P301L-Tau. We report that environmental stress triggers memory impairments in female, but not male, P301L-Tau transgenic mice. Furthermore, stress elevates levels of caspase-3-truncated Tau and insoluble Tau aggregates exclusively in the female hippocampus while it also alters the expression of the molecular chaperones Hsp90, Hsp70, and Hsp105, thus favoring accumulation of Tau aggregates. Our findings provide new insights into the molecular mechanisms through which clinically-relevant precipitating factors contribute to the pathophysiology of AD. Our data point to the exquisite sensitivity of the female hippocampus to stress-triggered Tau pathology.

Zoological Science, 2003

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Zoological Science, 1999

As the first step to study relationships between development and learning in the molluscan centra... more As the first step to study relationships between development and learning in the molluscan central nervous system, we examined developmental changes in acquisition and retention of a conditioned taste aversion (CTA) in the pond snail, Lymnaea stagnalis. We found that snails developed ability of a CTA as a long-term memory through three critical stages. Embryos in veliconcha started to respond to appetitive sucrose at the first critical stage. This response was in good agreement with morphological observations that embryos at this developmental stage seemed to be physically ready to eat. However, they could not associate this appetitive stimulus (conditioned stimulus: CS) with an aversive stimulus of KCl (unconditioned stimulus: UCS). At the second critical stage, embryos just before hatching acquired the CTA, but the conditioned response did not persist. Through this stage, they may acquire learning ability to safely seek out food in an external environment. At the third critical stage, immature snails with a 10 mm shell could use a long-term memory to maintain the conditioned response. This memory persisted for at least a month, showing that now they are able to maintain a long-term memory so that they can safely eat a variety of food when they cover wide territory to search for a mate. The present findings indicate that the development of learning ability in snails, which secures acquisition of better survival ability, is coincident with the major changes in their life cycle.

PLoS ONE, 2011

Squid can rapidly change the chromatic patterns on their body. The patterns are created by the ex... more Squid can rapidly change the chromatic patterns on their body. The patterns are created by the expansion and retraction of chromatophores. The chromatophore consists of a central pigment-containing cell surrounded by radial muscles that are controlled by motor neurons located in the central nervous system (CNS). In this study we used semi-intact squid (Sepioteuthis lessoniana) displaying centrally controlled natural patterns to analyze spatial and temporal activities of chromatophores located on the dorsal mantle skin. We found that chromatophores oscillated with miniature expansions/ retractions at various frequencies, even when the chromatic patterns appear macroscopically stable. The frequencies of this miniature oscillation differed between ''feature'' and ''background'' areas of chromatic patterns. Higher frequencies occurred in feature areas, whereas lower frequencies were detected in background areas. We also observed synchronization of the oscillation during chromatic pattern expression. The expansion size of chromatophores oscillating at high frequency correlated with the number of synchronized chromatophores but not the oscillation frequency. Miniature oscillations were not observed in denervated chromatophores. These results suggest that miniature oscillations of chromatophores are driven by motor neuronal activities in the CNS and that frequency and synchrony of this oscillation determine the chromatic pattern and the expansion size, respectively.

PLoS ONE, 2009

Background: The M 5 muscarinic acetylcholine receptor is known to play a crucial role in mediatin... more Background: The M 5 muscarinic acetylcholine receptor is known to play a crucial role in mediating acetylcholine dependent dilation of cerebral blood vessels. Previously, we reported that male M 5 muscarinic acetylcholine knockout mice (M5R 2/2 mice) suffer from a constitutive constriction of cerebral arteries, reduced cerebral blood flow, dendritic atrophy, and shortterm memory loss, without necrosis and/or inflammation in the brain. Methodology/Principal Findings: We employed the Magnetic Resonance Angiography to study the area of the basilar artery in male and female M5R 2/2 mice. Here we show that female M5R 2/2 mice did not show the reduction in vascular area observed in male M5R 2/2 mice. However, ovariectomized female M5R 2/2 mice displayed phenotypic changes similar to male M5R 2/2 mice, strongly suggesting that estrogen plays a key role in the observed gender differences. We found that 17b-estradiol (E2) induced nitric oxide release and ERK activation in a conditional immortalized mouse brain cerebrovascular endothelial cell line. Agonists of ERa, ERb, and GPR30 promoted ERK activation in this cell line. Moreover, in vivo magnetic resonance imaging studies showed that the cross section of the basilar artery was restored to normal in male M5R 2/2 mice treated with E2. Treatment with E2 also improved the performance of male M5R 2/2 mice in a cognitive test and reduced the atrophy of neural dendrites in the cerebral cortex and hippocampus. M5R 2/2 mice also showed astrocyte swelling in cortex and hippocampus using the three-dimensional reconstruction of electron microscope images. This phenotype was reversed by E2 treatment, similar to the observed deficits in dendrite morphology and the number of synapses. Conclusions/Significance: Our findings indicate that M5R 2/2 mice represent an excellent novel model system to study the beneficial effects of estrogen on cerebrovascular function and cognition. E2 may offer new therapeutic perspectives for the treatment of cerebrovascular insufficiency related memory dysfunction.

Learning & Memory, 1998

To determine the distribution of neurons that contribute to memory formation induced by odor-tast... more To determine the distribution of neurons that contribute to memory formation induced by odor-taste associative conditioning in the slug's brain, we examined neuronal activity of the central nervous system of the slug Limax marginatus using a fluorescent activity marker [Lucifer yellow (LY)]. When LY was injected into the body cavity just after the conditioning, many of the procerebral (PC) interneurons were labeled. The PC lobe was considered to play important roles in the olfaction of the slug, because the olfactory afferent fibers from both the inferior and the superior tentacular noses innervate it. Such strong dye-uptake activity of PC interneurons was not observed when LY was injected just after unpaired control treatment. Thus, it was suggested that enhancement of dye-uptake activity upon conditioning was caused by the association of a conditioning stimulus (CS) with an unconditioned stimulus (UCS). The distribution patterns of PC interneurons that were labeled by LY after...

Learning & Memory, 1998

We compared behaviorally and physiologically the olfactory responses of slugs (Limax marginatus) ... more We compared behaviorally and physiologically the olfactory responses of slugs (Limax marginatus) that had been subjected to aversive, appetitive, or unpaired training with food odors (carrot or cucumber). In the aversive training, the slugs were exposed to the food odor as a conditioned stimulus (CS), and then quinidine sulfate solution as an unconditioned stimulus (UCS) was immediately applied to the lip of the slugs. This training caused a decrease in preference level for the CS. The unpaired training, in which the CS and the UCS were presented to the slugs with a 5-min interval, induced no change in the preference level for the CS. In the appetitive training, the slugs were allowed to eat the CS odor source without UCS application. When we used nonstarved slugs, it was found that the preference level for the CS increased upon the appetitive training. These results indicate that each training changed the preference for the odors in a characteristic manner. In the physiological exp...

PloS one, 2008

PLoS ONE: an inclusive, peer-reviewed, open-access resource from the PUBLIC LIBRARY OF SCIENCE. R... more PLoS ONE: an inclusive, peer-reviewed, open-access resource from the PUBLIC LIBRARY OF SCIENCE. Reports of well-performed scientific studies from all disciplines freely available to the whole world.

Activation of GSK-3b is presumed to be involved in various neurodegenerative diseases, including ... more Activation of GSK-3b is presumed to be involved in various neurodegenerative diseases, including Alzheimer's disease (AD), which is characterized by memory disturbances during early stages of the disease. The normal function of GSK-3b in adult brain is not well understood. Here, we analyzed the ability of heterozygote GSK-3b knockout (GSK+/2) mice to form memories. In the Morris water maze (MWM), learning and memory performance of GSK+/2 mice was no different from that of wild-type (WT) mice for the first 3 days of training. With continued learning on subsequent days, however, retrograde amnesia was induced in GSK+/2 mice, suggesting that GSK+/2 mice might be impaired in their ability to form long-term memories. In contextual fear conditioning (CFC), context memory was normally consolidated in GSK+/2 mice, but once the original memory was reactivated, they showed reduced freezing, suggesting that GSK+/2 mice had impaired memory reconsolidation. Biochemical analysis showed that GSK-3b was activated after memory reactivation in WT mice. Intraperitoneal injection of a GSK-3 inhibitor before memory reactivation impaired memory reconsolidation in WT mice. These results suggest that memory reconsolidation requires activation of GSK-3b in the adult brain.

Background: Tauopathies are characterized by intracellular deposition of the microtubule-associat... more Background: Tauopathies are characterized by intracellular deposition of the microtubule-associated protein tau as filamentous aggregates. The rTg4510 mouse conditionally expresses mutant human tau protein in various forebrain areas under the Tet-off expression system. Mice develop neurofibrillary tangles, with significant neuronal loss and cognitive deficits by 6 months of age. Previous behavioral and biochemical work has linked the expression and aggregates of mutant tau to functional impairments. The present work used manganese-enhanced magnetic resonance imaging (MEMRI) to investigate basal levels of brain activity in the rTg4510 and control mice. Results: Our results show an unmistakable curtailment of neural activity in the amygdala and hippocampus, two regions known for their role in memory formation, but not the cortex, cerebellum, striatum and hypothalamus in tau expressing mice. Conclusion: Behavioral impairments associated with changes in activity in these areas may correspond to age progressive mutant tau P301L-induced neurodegeneration.

PloS one, 2014

In recent years, the study of resting state neural activity has received much attention. To bette... more In recent years, the study of resting state neural activity has received much attention. To better understand the roles of different brain regions in the regulation of behavioral activity in an arousing or a resting period, we developed a novel behavioral paradigm (8-arm food-foraging task; 8-arm FFT) using the radial 8-arm maze and examined how AcbC lesions affect behavioral execution and learning. Repetitive training on the 8-arm FFT facilitated motivation of normal rats to run quickly to the arm tips and to the center platform before the last-reward collection. Importantly, just after this point and before confirmation of no reward at the next arm traverse, locomotor activity decreased. This indicates that well-trained rats can predict the absence of the reward at the end of food seeking and then start another behavior, namely planned resting. Lesions of the AcbC after training selectively impaired this reduction of locomotor activity after the last-reward collection without chan...